Moisture-resistant flameproofed product and method of making same



Patented Oct- 17, 1950 Mo srunp-nnsrsrm'r Filmer-poorer) rnoooor AND METHOD or MAKING SAME Oscar ildelstein, Hamden, Conm, assignor to The Pond Lily Company, a corporation of Connecticut No Drawing. Application November 19, 1946, Serial No. 710,944

6 Claims. (01. 117-437) This invention relates to the fiame proofing of cellulosic materials and more particularly to the flameroofing of cellulosic textile fibers and fabrics which endures or survives the exposure of said fibers and fabrics to water and/or moistilre.

It has long been recognized that certain classes {of compounds when applied to such materials possess the ability to render the fabric or fibers flame-proof, i a, incapable of supporting combustion exce t in the presence of an independent heat source. Thus compounds such as phosphorus-containing acids, certain phosphates, sulfamic acid, certain sulfamates, sulfuric acid, certain sulfates and various other compounds have been proposed as fire retardants; and most of these compounds, and more articularly the phosphorus containing compounds, produce an initiall satisfactory fiame-proorlng effect when ap lied to a textile material in the roper proportions. However, flame-proofing compounds of this type are too easily removed from a fabric or rendered less effective as flame-proofing agents by water, for example, by a single immersion even in cold wa ter. Furthermore, the flame-proofing effect produced by such compounds is diminished when the fabric is exposed to a moist atmosphere for prolonged or recurring periods of time The susceptibility of fabrics treated with these fiame-proofing agents to deterioration or loss of their fiameroof quality is a serious defect, since there are many fields of use wherein it is essential to have a flame-proofed fabric which retains its flameproofing effect after washing or after continued or repeated exposure to moisture.

Previous attempts to produce a suiliciently durable or water -resistant or surviving flame-proofi'ng effect on textile fibers and fabrics have not been wholly successful. In a number of cases efforts have been made to impregnate fabrics with both conventional fire-retardant compounds of the kinds above suggested and synthetic or natural resins with a view to coating the fibers with a layer of the resin that is impervious to moisture and thereby preventing leaching out of the flameproofing agent. so far as I am aware, these prior attempts have been unsuccessful in producing a flameroofing effect that is water resistant to a commerciall acceptable degree. Moreover such prior processes are open to the further objection that they render the treated fabric stiff and in some cases brittle.

Accordin ly, among the objects of the present invention are to provide an impro edfame-proofing process capable of producing a flame-proofed product wherein the character of the flame-proofing is such that it is durable, i. e., resistant to the action of water in either vapor or liquid form; to reduce the combustibility of cellulosic materials: to produce a flame-proofed fabric that can be exposed to moisture over extended periods and that can be washed in hot or cold water, mild soap solutions, and dry cleaning solvents without losing its flame-proofing properties; to provide a process for producing such a fiame-proofed product; and to provide a process for rendering textile materials durable flameproof without materially detracting from the desirable qualities of the fabric such as softness, strength, appearance and the like. Other objects of the invention will be in part obvious and in part pointed out hereinafter.

In one of its broader aspects, the method of the present invention comprises impregnating a cellulosic material such as a cotton fabric with an effective flame-retardant compound and a compound selected from the group consisting of urea and dicyandiamide and thereafter rendering the resulting flame-proof quality of said fabric resistant to water and moisture by heat treating the impregnated material at a relatively high temperature for a relatively short period of time or at a relatively lower temperature for a sufficiently long period of time to produce said enduring effect. I have discovered that when a cotton fabric is impregnated with appropriate quantitles of a suitable flame-retardant, which may be water soluble, and either urea and/or dicyandlamide and is thereafter heated under conditions to produce a substantially water-insoluble reaction product on the fibers of the fabric, the fabric acquires a waterand moistureresistant flame-proofness that remains substantially as effective after exposure to water or moisture as when initially applied to the material.

The temperature and time of heat treatment required to produce this result on a given fabric are inversely related, that is, the higher the temperature, the less heat applying time is required to produce the desired durability of the flameproofing of the fabric; and the lower the temperature, the longer the heat applying time required to produce the desired durability thereof. The preferred range of temperatures is relatively high. Thus I have found that the heat treatment is preferably carried out at a temperature of at least about 325 F. and may, in respect to a given fabric, be advantageously carried out at a temperature just below that at which the material scorches. Hence, the effective upper limit of the temperature range or the maximum permissible temperature that may be used in carrying out the present method is that Just short of the scorching temperature of the goods. This maximum temperature will, of course, vary to some extent with the type of fabric that is being treated and with the period of time during which it is maintained at a particular temperature. Said maximum permissible temperature, and similarly the maximum time of treatment that can be used for any particular type of fabric at any given temperature without scorching the fabric, may be easily determined by well known test procedures.

At temperatures of the order of 300 F. a typical fabric, such as the 52 1.32 yards per pound cotton duck, described in Example 1, infra, might require two to three minutes of heat treatment, whereas at a temperature of 400 F. to 450 F. only a few seconds may be required. I have successfully used temperatures as high as 525 F. in cases where a relatively rugged material, e. g., a heavy cotton duck, is heat treated for very short periods of time, say one or two seconds.

The relatively rapid heat treatment used in the present process is particularly desirable from a commercial standpoint. Since the heat treatment may, as to widely used fabrics and under proper conditions, be completed within a few seconds at temperatures of the order of 400 F. to 450 F., the application of heat may be effected with advantage in a fully continuous manner by passing the impregnated fabric over heated rotating rolls for example; and thus high production rates may be achieved. It will ordinarily be desirable to provide the rolls used for heating the fabric with internal burners to avoid the high steam pressures that would otherwise be involved in attaining the relatively high temperatures that are desirable. although of course any method of heating that is capable of producing the desired temperatures may be used, such as banks of infrared lamps or curing ovens of the type presently used in the textile industry, provided that the surfaces of the fabric in process of treatment are well ventilated, for the reasons set forth hereafter.

It has been found to be important in facilitating effective treatment that the gases or vapors evolved from the fabric during the application of heat thereto be promptly removed from the vicinity of the fabric surface. Thus, if the heat treatment is carried out at a given temperature under conditions which retard the removal of said evolved gases and vapors from the heating zone, a substantially longer period of time is required to eiiect the desired durable flameproofing than would be needed at that temperature if the gases and vapors were promptly removed or dispersed. Any unnecessarily extended period of heat treatment especially at elevated temperatures is undesirable both because of the time consumed and because it tends to decrease the strength of the material being treated. Hence, if the treatment is necessarily or more conveniently carried out in a confined space, it is desirable that the vicinity of those portions of the material under treatment be adequately ventilated to reduce the concentration of or remove said gases and vapors from said space.

I have found further that the strength of the treated fabric is more effectively maintained by treating the fabric at higher temperatures for shorter periods rather than at lower temperatures for longer periods. Although it is true, in

general, that an increase in temperature increases the tendency of the fabric to tender," it is also true that an increase in the period of heating has a similar effect upon the fabric. I have found that the tendency of increasingly higher temperatures to tender the fabric is more than offset by the decrease in tendering tendency resulting from the corresponding reduction in timeof treatment which may be effected as the temperature is raised. For example, a given impregnated fabric, as that specified in Example 1, infra, might be rendered durably flame-proof to a given extent by treatment either at 400 F. for 6 seconds or at 300 F. for 2 minutes; but the strength of the fabric would be more effectively maintained in the former case than in the latter case. Thus, as indicated above, I prefer to carry out the heat treatment step at temperatures of at least about 325 F.

Fire-retardant compounds useful for impregnating the fabric according to my invention include certain compounds conventionally used for flame-proofing, such as phosphoric acid, ammonium phosphates, sulfuric acid, ammonium sulfate, sulfamic acid and ammonium sulfamate. These are used in conjunction with a compound, which for the purposes of this disclosure, may be characterized as a fixative and which is selected from the group consisting of urea and dicyandi- These two fixatives appear to be amide. uniquely useful in producing a durable flameprooflng effect, particularly when used as indicated in the specific examples set forth hereafter. It has been found that other compounds chemically related to urea and dicyandiamide produce some slight degree of durability of the flame-proofing effect but do not produce a commercially acceptable product.

In order to point out more fully the nature of the present invention, the following specific examples are given to illustrate various modes of application of the method of the invention, the products resulting therefrom, and the characteristics of said products in terms of flame-proofness and the durability or resistance thereof to depletio n by moisture or from washing.

Example 1 An aqueous solution is prepared by dissolving 208 pounds of urea and 83 pounds of diammonium phosphate in sufll-cient boiling water to make 50 gallons of solution. A 52 inch wide, boiled and bleached cotton duck, 1.32 yards per pound, is impregnated with this solution on a three bowl pad at a temperature of about 180 F. After it leaves the solution, the fabric is squeezed to such an extent that it retains about 120% of its weight of'solution and is dried by passage over heated rolls, in the usual manner. The fabric is thereafter treated to produce the desired lasting flameproof characteristics by passage in contact with steel rolls heated to a surface temperature of 360 F. in such a manner as to be exposed thereto for a period of about 13 seconds, the rolls being so arranged that each side of the fabric bears upon a heated roll surface for about 6% seconds. The roll surface temperature referred to is the temperature indicated by a mercury-in-glass thermometer placed in contact with the roll and covered with a thick layer of asbestos. The heat treated fabric is now in satisfactory condition for some uses without further processing. However, for other purposes the fabric is washed free of any soluble salts that remain thereon and is passed in its wet condition through a 5% ammonia solution, then dried under usual drying conditions. The ammonia treatment, when used, ensures that any residual acid present in the fabric will be neutralized.

Said cotton duck treated in the manner described was tested for fiame-proofness in accordance with the A. A. T. C. C. test as set forth in the 1945 Yearbook of the American Association of Textile Chemists and Colorists. In carrying out this test, the treated fabric is suspended ver-' tically above a flame of predetermined character under predetermined and specified conditions for a period of 12 seconds, at the end of which period the flame is removed and the extent of afterflaming, after-glow, and charring of the fabric determined. After-flaming and after-glow are the intervals respectively between the time when the flame is removed and the time when flaming and after-glow of the fabric ceases. Charring is measured in this test by measuring the distance between the lower edge of the fabric that is exposed to the flame and the point vertically above the lower edge that is capable of sustaining a predetermined weight. Fabrics are considered satisfactorily resistant to fire if the after-flaming does not exceed 2 seconds and charring does not extend more than 3.5 inches into the fabric.

The cotton duck of Example 1 in its initial flame-proofed condition, 1. e., after washing with water and ammonia solution, when tested in accordance with this test showed zero (0) afterflaming and zero (0) after-glow. The char measured 2.3 inches. This cloth was then subjected to the following water exposure: A liter of water was brought to a boil and the heat turned oil.

A 100 gram sample of the cloth was immersed in the hot water and allowed to remain hour, after which it was squeezed through a tight laundry wringer. The cloth sample was then alternately immersed in cold water and squeezed seven times.

After drying, the washed sample was exposed to the atmosphere for a suflicient length of time to permit it to regain its normal moisture content and tested for fiame-proofness in accordance with said A. A. T. C. C. method and showed zero (0) after-flaming, zero (0) after-glow and a char measuring 2.3 inches. vigorous washing treatment the flame-proofness of the fabric was still completely satisfactory.

It was further found that the fabric treated for flame-proofness in accordance with the procedure of Example 1 could be washed with mild soap solutions and still retain substantial flameproofing properties. A sample of the cotton cloth treated as described above through the steps of washing free from soluble salts and treating with weak ammonia solution was immersed with gentle stirring for minutes in an aqueous solution containing .5% tallow chip soap, the solution being maintained at 105 F., The cloth was then rinsed in warm water twice with squeezes between and after the washings and tested for flameproofness. After this treatment it showed zero (0) flaming, zero (0) glow, and a char measuring 3.0 inches.

Example 2 rayon and 30% wool is passed through this solu- Thus after the tion, the solution being heated to about F., as in Example 1. Upon removal from the impregnating solution, the fabric is squeezed and dried at usual drying temperatures and is thereafter heat treated by passage in contact with rolls heated at about 300 F. for about two minutes, one minute on each side. As in Example 1, the heat treated fabric is washed free of soluble salts, treated with ammonia, and dried.

Said fabric treated according to the procedure of this example was tested for durability of flameproofness as in Example 1. The initial flameproofness was the same as that of the sample tested in Example 1, except that the char measured 2.7 inches. After the same number of hot and cold water washes the after-flaming was zero (0), the after-glow zero (0) and the char measured 2.8 inches.

Example 3 An aqueous solution is prepared by dissolving 280 pounds of urea and 10 gallons of 50% phosphoric acid in sufllcient boiling water to make 50 gallons of solution. A 38-inch, 2.68 yards per I pound mercerized cotton twill is impregnated with this solution, squeezed, dried at usual drying temperatures, and heat treated on rolls at 325 F. for 1.5 minutes (45 seconds on each side). As in the case of previous examples, the fabric is washed free of soluble salts, treated with ammonia, and dried.

When tested for durability of flame-proofness as in Example 1, and after showing initial flameproofness substantially the same as that of the sample tested in Example 1, except that the char measured 2.8 inches, this fabric showed zero (0) after-flaming, zero (0) after-glow and a char of 3.0 inches, after the hot and cold water washes of Example 1.

Example 4 An aqueous solution is prepared by dissolving 62 pounds 4 ounces of dicyandiamide and 83 pounds of diammonium phosphate in suflicient boiling water to give 50 gallons of solution. A 48-inch, vat dyed, olive drab #10 duck is impregnated with this solution, squeezed, dried at usual drying temperatures and heat treated on rolls at 400 F. for about 20 seconds; ten seconds on each side. It is then washed free of soluble salts, treated with ammonia and dried, as in the previous examples, and after drying is found to be durably flame-proofed.

The fabric as thus treated when tested for durability of flame-proofness, as in Example 1, showed thefsame initial extent of flame-proofness as the test pieces in said example except that the char measured 2.5 inches; and after the hot and cold water wash of Example 1 showed zero (0) after-flaming, an after-glow of one second; and the char measured 2.7 inches Example 5 heat treated at 360 F. for about 13 seconds.

After washing, ammonia treatment and drying, the cotton duck thus treated was tested for flame-proofness and durability thereof, as described in Example 1; and both the initial flame-proofness and flame-proofness after as in Example 1.

Example 6 An aqueous solution is prepared by dissolving 62.5 pounds of dicyandiamide, 8 pounds ounces of diammonium phosphate and 104 pounds of ammonium sulphate in water to form 50 gallons of solution. A bleached cotton duck of the type referred to in Example 1 is impregnated with this solution, squeezed and heat treated at 360 F. for one minute, seconds on each side.

After washing, ammonia treatment and drying, the cotton duck thus treated was tested for fiame-proofness and durability thereof in accordance with the procedure set forthin Example 1; and both the initial flame-proofness and fiame-proofness after washing with water were substantially the same in Example 1.

Example 7 An aqueous solution is prepared by dissolving 166- pounds of urea and 70 pounds of mono ammonium phosphate in water to form 50 gallons of solution. A inch wide 4.00 yards per initial flame-proofness was similar to that of Example 1, except that the char measured 2.8 inches, and after washing, the sample showed zero (0) after-flaming, zero (0) after-glow and 'a char that measured 3.0 inches.

The foregoing examples are intended to be illustrative only and favorable results may be obtained in effecting treatments of different kinds and weights of fabrics under widely varying conditions within the contemplated scope of the present invention.v The quantities of the fire-retardant compound and of the fixative employed per unit weight of treated fabric do not appear to be particularly critical so far as durability of the flame-proofness is concerned. In general the quantities of the fire-retardant compound used are of the same order of magnitude as, or in some instances somewhat greater than, those that have been conventionally used or recommended in the past for producing various degrees of flame-proofness. effective for some purposes and of satisfactory durability, as indicated by tests of the kind described above, may be achieved in treating, for example, a 40 inch 4.00 yards per pound spun rayon fabric with a solution containing one half the amount of urea and two thirds the amount of diammonium phosphate used in Example 1 in gallons of solution; but, in general, preferred results are obtained by using the relatively higher concentrations of the order indicated in the foregoing examples.

It may be pointed out that the step of drying the fabric after it has been impregnated with the solution of fire-retardant and fixative and before heat treatment at high temperature is not an essential step of the process, although under some circumstances it is desirably included. Thus, for example, if the heat treatment is effected by bringing a sfream of ho air ino contact with the fabric, no separate drying step is required,

It has, been found that flame-proofness or, more precisely, the drying or water removal step can be effectively combined with the high temperature heat treatment step. On the other hand where the high temperature heat treatment is to be carried out by bringing the fabric into contact with a heated metal surface, as of the heated rolls for example, omission of the drying step tends to cause the solution to fry on the heating surface and produce less uniform distribution of the solids within the fabric.

Under such circumstances it is usually desirable to include a more gradual drying step at relatively low temperature beforecarrying out the high temperature heat treatment of the present process.

Further, the steps of washing out the soluble salts and treating with an ammonia solution after the heat treatment step are not essential, but may be desirable in certain cases. It is evident that any soluble fire-retardant compound left in the goods after the heat treatment step provides to that extent an initial flame-proofing effect that supplements the durable flame-proofing effect produced by the present .process. This supplemental flame-proofing effect is of course non-durable. However, where the prospective conditions of use are such that the soluble material is not likely to be washed or leached out and the stiffness of the fabric due to the presence of the soluble material is not detrimental, it may be desirable to leave this soluble fire-retardant compound in the goods and thus utilize its supplemental flame-proofing effect, thereby also eliminating the extra process steps of washing the fabric with Water and treating with ammonia.

On the other hand the softness and flexibility of the goods may be improved by washing out the residual soluble material after heat treatment and where such softness and flexibility are desired, the washing step is advantageously used.

It is to be understood that the heat treatment described in the specific examples is that treatment required to produce a product which will, after washing in accordance with the specified procedure, at least satisfy the A. A. T. C. C. test. It is evident that there may be cases in which a lesser degree of flame-proofness and/or a lesser degree of durability of flame-proofness than that given by the procedures of the specific examples 'will be satisfactory. In such cases the lesser degree of fiame-proofness and/or durability of fiame-proofness may be obtained by appropriate reduction in the quantity of flame-retardant used or in the temperature and/or time of heat treatment.

The flame-proofing agent and the fixative may be applied in separate steps and either may be applied first. However, it will ordinarily be desirable and economical to use a single step impregnation in a bath containing both the flameproofing agent and the fixative in solution. As indicated in Examples 2, 5, and 6, more than one fire-retardant compound and more than one fixative may be incorporated in the impregnating solution if desired. Further, it is to be understood that various modifying agents may be incorporated in the impregnating bath if desired. Thus, well-known plasticizers, such as turkey red oil, ammonium stearate and other fatty compounds may be incorporated to soften and strengthen the cloth; and conventional inhibitors such as 2-amino, 2-methyl, 1,3 propanediol; sucrose, lactose, glucose; ammonium borate, diethylene triamine; ethylene diamine and other buffering agents may be used to improve the physical characteristics of the finished cloth.

Other textile finishing assistants of various types and for various purposes may be included in the impregnation bath in cases where their presence does not prevent attainment of the desired objectives of the invention. For example, wetting agents may be used as assistants when impregnating grey goods or other fabrics diflicult to wet. Also finishing assistants such as water repellants may be included in the impregnation bath or they may be applied after the flameproofing effect has been fixed by heat treatment or after the fabric has been washed subsequent to heat treatment.

As indicated by the foregoing specific examples, the present process produces a cellulosic fiber fabric having a flame-proofing property that is unusually enduring or resistant to moisture. Moreover, this lasting flame-proofing effect is achieved without substantial impairment of the fabric for usual purposes, that is to say, the softness or flexibility of the fabric is retained and its strength is only slightly reduced.

The process is particularly well adapted for continuous operation at high production rates. The single impregnation step can be carried out by simple immersion of a continuous strip of fabric; and the heat treatment, because of its brevity, can be effected by passage of the continuous strip in heat exchange relation to hot rolls. The washing and ammonia treatment steps can likewise be carried out continuously. The impregnants used are ordinarily inexpensive and easily available.

Since various embodiments of the product according to the present invention are contemplated and since many changes might be made in the embodiments disclosed herein, and in the procedures employed in producing said embodiments, it is to be understood that the foregoing description is to be interpreted as illustrative only and not in a limiting sense.

I claim:

1. A method of producing on a textile material composed essentially of cellulose a flame-proofing effect resistant to water, comprising the steps of impregnating said material with an aqueous solution containing as its essential active ingredients a fire-retardant compound selected from the group consisting of phosphorus-containing acids, sulphamic acid, sulphuric acid and their ammonium salts, and a fixative selected from the group consisting of urea and dicyandlamide, squeezing and drying said material, heating said material at a temperature between 300 F. and a temperature just below the scorching temperature of said material for a period of between a few seconds and a few minutes, and continuously exhausting gaseous reaction products from the surface of said material during said heating period.

2. A method of producing on a textile material composed essentially of cellulose a flame-proofing effect resistant to water, comprising the steps of impregnating said material with an aqueous solution containing as its essential active ingredients by the process of claim 4.

10 a fire-retardant compound selected from the group consisting of phosphorus-containing acids, sulphamic acid, sulphuric acid and their ammonium salts and a fixative which is urea, squeezing and drying said material, heating said material at a temperature between 300 F. and a temperature just below the scorching temperature of said material for a period of between a few seconds and a few minutes, and contimiously exhausting gaseous reaction products from the surface of said material during said heating period.

3. A method of producing on a textile material composed essentially Of cellulose a flame-proofing efiect resistant to water comprising the steps of impregnating said material with an aqueous solution containing as its essential active ingredients a fire-retardant compound selected from the group consisting of phosphorus-containing acids, sulphamic acid, sulphuric acid and their ammonium salts and a fixative which is dicyandiamide, squeezing and drying said material, heating said material at a temperature between 300 F. and a temperature just below the scorching temperature of said material for a. period of between a few seconds and a few minutes, and continuously exhausting gaseous reaction products from the surface of said material during said heating period.

4. A method of producing on a textile material composed essentially of cellulose a flame-proofing effect resistant to water, comprising the steps of impregnating said material with an aqueous solution containing as its essential active ingredients urea and diammonium phosphate,

squeezing and drying said material, heating said material at a temperature between 00 F. and a temperature just below the scorching temperature of said material for a period of between a few seconds and a few minutes, and continuously exhausting gaseous reaction products from the surface of said material during said heating period.

5. As a new article of manufacture an improved flame-proofed cellulose textile material wherein the flame-proofing is of a character that is retained after immersion of the material in water, said material being the product produced by the process of claim 1.

6. As a new article of manufacture an improved flame-proofed cellulose textile material wherein the flame-proofing is of a character that is retained after the immersion of the material in water, said material being the product produced OSCAR EDELSTEIN.

REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS Ford et a1. Sept. 27, 949 

1. A METHOD OF PRODUCING ON A TEXTILE MATERIAL COMPOSED ESSENTIALLY OF CELLULOSE A FLAME-PROOFING EFFECT RESISTANT TO WATER, COMPRISING THE STEPS OF IMPREGNATING SAID MATERIAL WITH AN AQUEOUS SOLUTION CONTAINING AS ITS ESSENTIAL ACTIVE INGREDIENTS A FIRE-RETARDANT COMPOUND SELECTED FROM THE GROUP CONSISTING OF PHOSPHORUS-CONTAINING ACIDS, SULPHAMIC ACID, SULPHURIC ACID AND THEIR AMMONIUM SALTS, AND A FIXATIVE SELECTED FROM THE GROUP CONSISTING OF UREA AND DICYANDIAMIDE, SQUEEZING AND DRYING SAID MATERIAL, HEATING SAID MATERIAL AT A TEMPERATURE BETWEEN 300*F. AND A TEMPERATURE JUST BELOW THE SCORCHING TEMPERATURE OF SAID MATERIAL FOR A PERIOD OF BETWEEN A FEW SECONDS AND A FEW MINUTES, AND CONTINUOUSLY EXHAUSTING GASEOUS REACTION PRODUCTS FROM THE SURFACE OF SAID MATERIAL DURING SAID HEATING PERIOD. 